The present invention relates to a process for the preparation of ketimines, which are suitable as starting materials for the preparation of pharmaceutical active ingredients having antidepressant properties, for example sertraline.
Processes for the preparation of ketimines are described, for example, in U.S. Pat. No. 4,536,518 and U.S. Pat. No. 4,855,500.
The process for the preparation of ketimines disclosed in U.S. Pat. No. 4,536,518 (columns 9/10, Example 1(F)) comprises reaction of the ketone in an aprotic solvent, for example tetrahydrofuran, with methylamine in the presence of titanium tetrachloride, with cooling. A disadvantage of that process is the need to work with tetrahydrofuran, which is readily combustible, and with titanium tetrachloride, which is not innocuous from an ecological standpoint. In addition, the procedure is expensive, because the reaction is carried out with cooling. A further disadvantage of the process concerns the working up. The product has to be precipitated with additional hexane.
The process for the preparation of ketimines disclosed in U.S. Pat. No. 4,855,500 (columns 5/6, claim 1) comprises reaction of the ketone in an aprotic solvent, for example methylene chloride, toluene or tetrahydrofuran, with anhydrous methylamine in the presence of molecular sieve, with cooling.
That process, too, has the disadvantage of the need to work, under anhydrous conditions, with solvents that are not innocuous from an ecological standpoint, such as methylene chloride, or with readily combustible solvents, such as tetrahydrofuran. The molecular sieve used is expensive and has to be recycled in an additional step. A further disadvantage of the process is that the molecular sieve needs to be removed and the product has to be precipitated with additional hexane.
U.S. Pat. No. 5,019,655 describes a one-step process for the preparation of 4-dichlorophenyl-1-tetralones having a degree of purity of from 98 to 99%. It is disclosed that a plurality of recrystallisation operations are required at the ketone stage, using large amounts of solvents, in order to achieve a degree of purity  greater than 99.5%.
The need therefore exists for the discovery of an efficient process for the preparation of ketimines that does not have the above-listed disadvantages, especially in relation to the solvents and recrystallisation steps used.
Surprisingly, it has now been found that the desired degree of purity of ketimines can be achieved by carrying out the recrystallisation at the imine stage and using sertralone, precipitated in crude form, in the imine synthesis. At the same time high yields are achieved, and substantially smaller amounts of solvents are sufficient for the recrystallisation.
The present invention accordingly relates to a process for the preparation of compounds of formula 
reacting an isomeric mixture consisting of from 75 to 95% of a compound of formula (2a) and from 5 to 25% of a compound of formula (2b) with methylamine, in a suitable solvent, using suitable methods of isolation to form an enriched sertraline-imine isomeric mixture, consisting of  greater than 99% of a compound of formula (1a) and  less than 1% of a compound of formula (1b) (A2);
and then subjecting the sertraline-imine isomeric mixture obtained according to reaction route (A1) or (A2), in a suitable solvent, to recrystallisation (B), in accordance with the following scheme: 
xe2x80x83wherein in formulae (1a), (1b), (2a) and (2b)
R1, R2 and R3 are each independently of the others hydrogen, halogen, trifluoromethyl or C1-C4alkoxy.
The solvents preferably used for reaction routes (A1), (A2) and (B) are selected from
(a) C1-C24amines,
(b) C1-C12nitriles,
(c) C2-C24carboxylic acid esters,
(d) C3-C24ortho esters,
(e) C2-C24ethers,
(f) C1-C24alkanes,
(g) aromatic solvents,
(h) amides,
(i) sulfoxides,
(k) halogenated solvents,
(l) supercritical CO2, and
(m) protic solvents.
Especially preferred solvents (a) are selected from aliphatic monoamines, especially methylamine, nitrogen heterocycles, and aliphatic and aromatic, non-substituted or substituted secondary and tertiary mono-, di- and tri-amines.
Further preferred solvents (a) correspond to formula 
R3 is hydrogen; C1-C5alkyl; hydroxy-C1-C5alkyl; C5-C7cycloalkyl; non-substituted phenyl or phenyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; non-substituted phenyl-C1-C3alkyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro;
R4 and R5 are each independently of the other C1-C5alkyl; C5-C7cycloalkyl; hydroxy-C1-C5alkyl; non-substituted phenyl or phenyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; non-substituted phenyl-C1-C3alkyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; or R4 and R5 together with the nitrogen atom form a 3- to 6-membered heterocyclic radical.
There are furthermore preferably used solvents (a) that correspond to formula 
R6 and R8 are each independently of the other hydrogen; C1-C5alkyl; or C5-C7cycloalkyl,
R7 and R9 are each independently of the other C1-C5alkyl; C5-C7cycloalkyl; non-substituted phenyl or phenyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; non-substituted phenyl-C1-C3alkyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro, or
R6 and R7, R8 and R9, or R7 and R9, as the case may be, form a 3- to 6-membered heterocyclic radical; and
A2 is C1-C5alkylene.
The following may be mentioned as representative examples of solvents (a) for use in accordance with the invention:
as aliphatic monoamines, e.g. methylamine, dimethylamine, triethylamine, diethylamine, triethylamine, di-n-propylamine and tri-n-propylamine;
as nitrogen heterocycles, ethylene-imine, pyrrolidine, piperidine and morpholine,
as aliphatic diamines, e.g. N,N-dimethylethylenediamine and hexamethylenediamine;
as aromatic monoamines, e.g. N-methylaniline and N,N-dimethylaniline;
as substituted aromatic monoamines, e.g. o-, m- and p-toluidine, 2-, 3- and 4-chloroaniline, 2-, 3- and 4-nitroaniline;
as aromatic diamines, e.g. o-, m- and p-phenylenediamine.
Preferably used solvents (b) correspond to formula
R10xe2x80x94Cxe2x89xa1N,xe2x80x83xe2x80x83(5) wherein
R10 is straight-chain or branched C1-C12alkyl; C5-C7cycloalkyl; non-substituted phenyl or phenyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; non-substituted phenyl-C1-C3alkyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro.
Representative examples of that group of solvents include acetonitrile and benzonitrile.
As solvents (c) there are preferably used compounds of formula 
R12 and R13 are each independently of the other straight-chain or branched C1-C12alkyl;
C5-C7cycloalkyl; non-substituted phenyl or phenyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; non-substituted phenyl-C1-C3alkyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro.
Representative examples of such solvents include acetates, e.g. methyl acetate and ethyl acetate.
Solvents (d) preferably used according to the invention correspond to formula 
R14 is hydrogen; straight-chain or branched C1-C5alkyl; or C5-C7cycloalkyl; and
R15 is C1-C5alkyl.
Representative examples of such solvents include orthoformic acid C1-C3alkyl esters, especially orthoformic acid methyl or ethyl ester, and orthoacetic acid C1-C3alkyl esters, especially orthoacetic acid ethyl ester.
Solvents (e) preferably used according to the invention correspond to formula
R16xe2x80x94Oxe2x80x94R17,xe2x80x83xe2x80x83(8) wherein
R16 and R17 are each independently of the other straight-chain or branched C1-C12alkyl; or C5-C7cycloalkyl.
Representative examples of such solvents include dimethyl ether, diethyl ether, methyl ethyl ether, methyl n-propyl ether, methyl isopropyl ether, diisopropyl ether, dibutyl ether and tert-butyl methyl ether. Polyethers can also be used.
Solvents (f) preferably used according to the invention are saturated C6-C22hydrocarbons, e.g. hexane, neohexane, heptane, octane, isooctane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, heneicosane and docosane.
Solvents (g) preferably used according to the invention are benzene, toluene, xylene and xylene isomeric mixtures.
Solvents (h) preferably used according to the invention are especially aliphatic and aromatic amides corresponding to formula 
R18 and R19 are each independently of the other hydrogen; C1-C5alkyl; or C5-C7cycloalkyl, and
R20 is C1-C5alkyl; C5-C7cycloalkyl; non-substituted phenyl or phenyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; or non-substituted phenyl-C1-C3alkyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro.
Examples of solvents (i) correspond to formula
R21xe2x80x94(Sxe2x95x90O)xe2x80x94R22,xe2x80x83xe2x80x83(10) wherein
R21 and R22 are each independently of the other C1-C5alkyl; C5-C7cycloalkyl; non-substituted phenyl or phenyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; or non-substituted phenyl-C1-C3alkyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro.
Examples of solvent (k) correspond to formula
ClCR23R24R25,xe2x80x83xe2x80x83(11a)
Cl2CR26R27xe2x80x83xe2x80x83(11b) or
Cl3CR28,xe2x80x83xe2x80x83(11c) wherein
R23, R24, R25, R26, R27 and R28 are each independently of the others C1-C5alkyl; C5-C7cycloalkyl; non-substituted phenyl or phenyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro; or non-substituted phenyl-C1-C3alkyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups, by halogen or by nitro.
Representative examples of that class of solvents include dichloroethane, dichloropropane, trichloroethane; and also haloaromatic compounds, e.g. chlorobenzene and dichlorobenzene.
When supercritical CO2 is used, the reaction is carried out at a temperature Txe2x89xa7Tcrit and pxe2x89xa7pcrit in CO2 as solvent. Following the reaction, CO2 is evaporated off and the imine is discharged in the form of a solid.
The protic solvent (m) is preferably an alcohol that corresponds especially to formula
X(OH)bxe2x80x83xe2x80x83(12)
wherein
b is 1, 2, 3 or 4, and,
when b is 1,
X is C1-C8alkyl, C5-C8cycloalkyl or xe2x80x94CH2CH2(OCH2CH2)cR21,
c is 0, 1 or 2, and
R21 is C1-C4alkoxy, or,
when b is 2,
X is C2-C8alkylene or xe2x80x94CH2CH2(OCH2CH2)cxe2x80x94, c having the meanings given above, or,
when b is 3,
X is C3-C8alkanetriyl or N(CH2CH2)3, or,
when b is 4,
X is C4-C8alkanetetrayl.
A preferred meaning of X (when b=1) is, for example, C1-C6alkyl, especially C1-C4alkyl, e.g. ethyl or isopropyl.
A preferred meaning of X (when b=2) is, for example, C2-C6alkylene, especially C2-C4alkylene, e.g. ethylene.
Of particular interest is a process for the preparation of compounds of formula (1) in which the protic solvent is a compound of formula (12) wherein
b is 1 or 2, and,
when b is 1,
X is C1-C4alkyl or C5-C6cydoalkyl, or,
when b is 2,
X is C2-C4alkylene.
Alcohols that are relevant in practice are methanol, ethanol, isopropanol, n-butanol, ethylene glycol, methyl Cellosolve, ethyl Cellosolve, cyclohexanol, glycerol, diethylene glycol, triethanolamine, polyethylene glycol, sec-butanol, n-propanol and tert-butanol.
In the above definitions of the radicals R1 to R21:
C1-C12alkyl is a branched or unbranched hydrocarbon radical, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, 2-ethylbutyl, n-pentyl, isopentyl, 1-methylpentyl, 1,3-dimethylbutyl, n-hexyl, 1-methylhexyl, n-heptyl, isoheptyl, 1,1,3,3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl, 2-ethylhexyl, isooctyl, nonyl, decyl, undecyl or dodecyl;
C5-C8cydoalkyl is, for example, cyclopentyl, cycloheptyl, cyclooctyl or, preferably, cyclohexyl;
C1-C4alkoxy is a branched or unbranched hydrocarbon radical, for example methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy or tert-butoxy. Preference is given to methoxy;
C2-C18alkenyl is, for example, allyl, methallyl, isopropenyl, 2-butenyl, 3-butenyl, isobutenyl, n-penta-2,4-dienyl, 3-methylbut-2-enyl, n-oct-2-enyl, nodec-2-enyl, isododecenyl, n-dodec-2-enyl or n-octadec-4-enyl;
C3-C12alkynyl is C3-C12alkenyl that is doubly unsaturated one or more times, wherein the triple bonds may optionally be isolated or conjugated with one another or with double bonds, e.g. 1-propyn-3-yl, 1-butyn-4-yl, 1-pentyn-5yl, 2-methyl-3-butyn-2-yl, 1,4-pentadiyn-3-yl, 1,3-pentadiyn-5-yl, 1-hexyn-6-yl, cis-3-methyl-2-penten-4-yn-1-yl, trans-3-methyl-2-penten-4-yn-1-yl, 1,3-hexadiyn-5-yl, 1-octyn-8-yl, 1-nonyn-9-yl or 1-decyn-10-yl;
C2-C8alkylene is a branched or unbranched radical, for example ethylene, propylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene or octamethylene.
Alkanetriyl having from 3 to 8 carbon atoms is derived from an alkane having from 3 to 8 carbon atoms, has 3 hydrogen atoms missing and is, for example 
Glyceryl is preferred.
C4-C8Alkanetetrayl is derived from an alkane having from 4 to 8 carbon atoms, has 3 hydrogen atoms missing and is 
Pentaerythrityl is preferred.
Halogen is, for example, chlorine, bromine or iodine. Chlorine is preferred.
It is furthermore possible for further solubilising or solubility-inhibiting additives (e.g. toluene, cyclohexane) to be added.
The present process may optionally be carried out in the presence of a catalyst. Preferred catalysts for the process for the preparation of compounds of formula (1) are protonic acids, Lewis acids, aluminium silicates, ion exchange resins, zeolites, naturally occurring layer silicates and modified layer silicates.
Protonic acids are preferred.
Suitable protonic acids include, for example, acids of inorganic or organic salts, e.g. hydrochloric acid; sulfuric acid; phosphoric acid or sulfonic acids, for example methanesulfonic acid, p-toluenesulfonic acid or camphor-10-sulfonic acid.
A suitable Lewis acid is, for example, scandium tristriflate [Sc(OTf)3].
Suitable aluminium silicates include, for example, those widely used in the petrochemical industry and referred to also as amorphous aluminium silicates. Such compounds contain approximately from 10 to 30% silicon dioxide and from 70 to 90% aluminium oxide.
Suitable ion exchange resins include, for example, styrene-divinylbenzene resins that in addition carry sulfonic acid groups, e.g. Amberlite 200(copyright) and Amberlyst(copyright) from Rohm and Haas and Dowex 50(copyright) from Dow Chemicals; perfluorinated ion exchange resins, e.g. NafionH(copyright) from DuPont; and other superacidic ion exchange resins as described by T. Yamaguchi, Applied Catalysis, 61, 1-25 (1990) or M. Hino et al., J. Chem. Soc. Chem. Commun. 1980, 851-852.
Suitable zeolites include, for example, those that are widely used in the petrochemical industry as cracking catalysts and that are known in the form of crystalline silicon-aluminium oxides having various crystal structures. Special preference is given to the faujasites from Union Carbide, e.g. Zeolite X(copyright), Zeolite Y(copyright) and Ultrastable Zeolite Y(copyright), Zeolite Beta(copyright) and Zeolite ZSM-12(copyright) from Mobil Oil Co. and Zeolite Mordenit(copyright) from Norton.
Suitable naturally occurring layer silicates are also called xe2x80x9cacid earthsxe2x80x9d and include, for example, bentonites and montmorillonites which, on an industrial scale, are broken down, ground, treated with mineral acids and calcined. Especially suitable naturally occurring layer silicates are the Fulcat(copyright) types from Laporte Adsorbents Co., e.g. Fulcat 22A(copyright), Fulcat 22B(copyright), Fulcat 20(copyright), Fulcat 30(copyright) and Fulcat 40(copyright); and the Fulmont(copyright) types from Laporte Adsorbents Co., e.g. Fulmont XMP-3(copyright) and Fulmont XMP-4(copyright). An especially preferred catalyst for the process according to the invention is Fulcat 22B(copyright). The other Fulcat(copyright) types and Fulmont(copyright) types are likewise to be classified in that preferred group, however, because only slight differences exist between the individual types, such as, for example, the number of acid centres.
Modified layer silicates are also called xe2x80x9cpillared claysxe2x80x9d and are derived from the above-described naturally occurring layer silicates, comprising in addition, between the silicate layers, oxides of, for example, zirconium, iron, zinc, nickel, chromium, cobalt or magnesium. That type of catalyst is widely mentioned in the literature, e.g. as described by J. Clark et al., J. Chem. Soc. Chem. Com. 1989, 1353-1354, but is manufactured by only very few companies. Especially preferred modified layer silicates include, for example, Envirocat EPZ-10(copyright), Envirocat EPZG(copyright) and Envirocat EPIC(copyright) from Contract Chemicals.
Special preference is given to a process for the preparation of compounds of formula (1a) wherein the catalyst is a sulfonic acid, especially p-toluenesulfonic acid, methanesulfonic acid or camphor-10-sulfonic acid.
The molar ratio of the amount of catalyst used to the amount of methylamine used is advantageously from 0.001:1 to 1:1, especially from 0.01:1 to 0.5:1, e.g. from 0.05:1 to 0.1:1.
A molar ratio of the amount of catalyst to the amount of methylamine of 1:1 means that the methylamine can be used in the process according to the invention also in the form of a salt, e.g. methylamine hydrochloride.
The reaction steps (A1) and (A2) are preferably carried out at a temperature of from 20 to 150xc2x0 C., especially from 30 to 100xc2x0 C., where appropriate under slight pressure.
The proportion of starting compounds in the reaction mixture is in the range from 5 to 70% by weight, preferably from 30 to 60% by weight.
Especially preferably, the reaction is carried out using a large molar excess of methylamine.
Special preference is therefore given to a process for the preparation of compounds of formula (1a) wherein the molar ratio of the amount of compound of formula (2a and 2b) to the amount of methylamine is from 1:1 to 1:1000, especially from 1:1.05 to 1:50, e.g. from 1:1.5 to 1:15.
The methylamine can be used in the form of methylamine gas or in the form of a solution in an appropriate solvent.
Of special interest is a process variant in which the reaction can be carried out in pure methylamine under pressure, that compound being used simultaneously as solvent and reagent.
Also of special interest is a process for the preparation of compounds of formula (1a) wherein the compound is continuously crystallised out of the reaction medium to a varying extent during the preparation process and subsequently filtered off.
Also of special interest is a process for the preparation of compounds of formula (1a) wherein the filtrate is used in a further reaction for the preparation of compounds of formula (1a). In that procedure the consumed amounts of the compound of formula (2a) and of methylamine are replenished. Preference is given to from 2 to 10 filtrate-recycling operations.
The process according to the invention is accordingly suitable as a continuous process for the preparation of compounds of formula (1a).
The water formed during the process can optionally be bound to an additional water binder, for example a molecular sieve or ortho ester, e.g. orthoformic acid trimethyl ester.
For isolation of non-enriched sertraline-imine isomeric mixtures (reaction route A1), when the reaction is complete the solvent is distilled off, or methylamine or other gaseous amines are released, and the residue obtained is dried.
For isolation of enriched sertraline-imine isomeric mixtures (A2), the reaction mass is cooled, the suspension is filtered, and the filter cake is washed with the solvent. The product is then dried.
The solvents used for recrystallisation (B) are selected from
(a) C1-C24amines,
(b) C1-C12nitriles,
(c) C2-C24carboxylic acid esters,
(d) C3-C24ortho esters,
(e) C2-C24ethers,
(f) C1-C24alkanes, especially C6-C24alkanes,
(g) aromatic solvents,
(h) amides,
(i) sulfoxides,
(k) halogenated solvents,
(l) supercritical CO2,
(m) protic solvents, and
(n) C2-C24ketones.
C2-C24Ketones (=component (n)) correspond especially to formula 
R22 and R23 are each independently of the other branched or unbranched C1-C12alkyl; C5-C7cycloalkyl; C2-C12alkenyl; C3-C12alkynyl; non-substituted phenyl or phenyl-C1-C3alkyl, or phenyl or phenyl-C1-C3alkyl substituted by one or more C1-C5alkyl groups;
A1 is a direct bond; or C1-C5alkylene; and
n is 0; or 1.
Representative examples of that group of ketones include, e.g., aliphatically saturated ketones, e.g. propanone (acetone), butanone (methyl ethyl ketone) and 2-pentanone (methyl propyl ketone); cycloaliphatically saturated ketones, e.g. cyclopentanone, cyclohexanone and cycloheptanone (suberone); aliphatically unsaturated ketones, e.g. 3-buten-2-one, 1,4-pentadien-3-one, 3-pentyn-2-one; aromatic ketones, e.g. benzophenone; aromatic-aliphatic ketones, e.g. methyl phenyl ketone (acetophenone) and propiophenone; diketones, e.g. 2,3-butanedione, 2,4-pentanedione and 2,5-hexanedione; and aromatic diketones, e.g. diphenylethanedione (benzil). In an especially preferred embodiment, recrystallisation (B) is carried out from the same solvent as reaction (A1) or (A2).
The solvents employed in accordance with the invention may be used in the form of individual compounds or in the form of mixtures of two or more individual compounds from the same or different solvent groups (a)-(n).
Recrystallisation (B) is preferably carried out by recrystallising the sertraline-imine isomeric mixture or the enriched sertraline-imine isomeric mixture under reflux. For that purpose the sertraline-imine obtained according to (A1) or (A2), in a suitable solvent, is introduced into a suitable reaction vessel fitted with a stirrer and a reflux condenser. The reaction mass is heated at reflux temperature in an inert gas atmosphere, with stirring, until a clear solution is obtained. The solution is cooled to the appropriate isolation temperature, the product slowly precipitating. The suspension is filtered, and the filter cake is washed with the solvent and dried. Isomerically pure ( greater than 99.9%) sertraline-imine of formula (1a) is obtained in a yield of from 80 to 90%, having a sertralone content of from 0.1 to 0.3% (HPLC), a catalyst contamination of xe2x89xa60.001% and a water content of from 0.1 to 0.3%.
In a further process variant, recrystallisation (B) of the sertraline-imine isomeric mixture or of the enriched sertraline-imine isomeric mixture is carried out under pressure. For that purpose the sertraline-imine obtained by (A1) or (A2) and the solvent are introduced into a suitable pressurized reactor fitted with a stirrer. The reactor is sealed under a nitrogen atmosphere. The stirrer is started and the reaction mixture is heated at the desired reaction temperature until a clear solution is obtained. The solution is cooled to the appropriate isolation temperature, the product slowly precipitating. The suspension is filtered, and the filter cake is washed with the solvent and dried.
The dissolution temperatures in the solvents selected are in the range from 30 to 150xc2x0 C., preferably from 50 to 150xc2x0 C. and most preferably from 70 to 120xc2x0 C.
According to the boiling points of the solvents listed, recrystallisation (B) can be carried out at normal pressure under reflux, or at elevated pressure, generally in the range from 0 to 10 bar, preferably from 0 to 3 bar.
The cooling gradients are in the range from 0.005 to 10xc2x0 C./min., preferably from 0.05 to 10xc2x0 C./min and most preferably from 0.1 to 1xc2x0 C./min.
The isolation temperatures are in the range from xe2x88x9220 to 40xc2x0 C., preferably from 0 to 25xc2x0 C.
The concentrations of sertraline-imine in the clear solution are in the range from 5 to 40% by weight, preferably from 15 to 20% by weight.
Adsorbents such as activated charcoal or adsorber resins may be added during the procedure for the purpose of removing impurities that impart colour. Such substances are added in amounts of from 1 to 10% of the clear solution and are removed, while hot, by filtration prior to the crystallisation procedure.
By means of the recrystallisation, it is possible both to improve the product purity and to remove impurities that interfere with the further reaction, such as water or catalyst residues.
The present invention relates also to a process for the preparation of optically pure (cis)- and/or (trans)-sertraline or enantiomerically enriched mixtures of (cis)- and (trans)-sertraline. The process comprises the following reaction steps (I) to (III):
(I) reaction of an isomeric mixture, consisting of from 75 to 95% of formula (2a) and from 25 to 5% respectively of formula (2b), to form the sertraline-imine of formula (1a), corresponding to the process according to claim 1,
(II) subsequent cis-selective hydrogenation using noble metal catalysts or other catalysts based on copper or nickel, to form cis-sertraline-enriched mixtures of racemic cis- and trans-sertraline,
(III) subsequent racemate cleavage based on mandelic acid for the selective preparation of the desired enantiomerically pure cis-isomer.
Starting from crude sertraline-ketone (isomeric mixture of the compounds of formulae (2a) and (2b)), sertraline-imine is prepared in accordance with the process described in claim 1. The imine is converted to cis-sertraline-enriched mixtures of racemic cis- and trans-sertraline in a subsequent cis-selective hydrogenation using noble metal catalysts or other catalysts based on copper or nickel with a wide variety of supports, e.g. carbon, Alox, aluminium oxide, silica, calcium carbonate, barium carbonate, barium sulfate etc.
The desired enantiomerically pure cis-isomer can be selectively crystallised in a subsequent racemate cleavage based on mandelic acid.
The optically pure amine is freed using sodium hydroxide solution and, as a hydrochloride, is converted in suitable solvents into the desired polymorphous form.